Apparatus for preventing deflection of substrate tube

ABSTRACT

An apparatus for producing an optical fiber preform to perform the deposition process by modified chemical vapor deposition. The Apparatus comprises a main heat source location sensor ( 800 ) for detecting the location of a main heat source for heating a substrate tube  100 , an additional supporting device control part ( 1000 ) wiredly or wirelessly connected to the main heat source location sensor ( 800 ), and an additional supporting device ( 1100 ) wiredly or wirelessly connected to the additional supporting device control part ( 1000 ) for supporting the substrate tube ( 100 ). The present invention reduces the effective length of the substrate tube ( 100 ) by additionally supporting the substrate tube ( 100 ), thereby minimizing the deflection of the substrate tube ( 100 ). Particularly, it is possible to considerably reduce the deflection of the substrate tube at its initial part and thus to achieve a high deposition efficiency. Accordingly, it is possible to mass-produce an optical fiber preform of high quality.

TECHNICAL FIELD

The present invention relates to a method for producing an optical fiberpreform by modified chemical vapor deposition (MCVD), and moreparticularly to an apparatus for producing an optical fiber preform witha minimized deflection of a substrate tube (quartz) and a method forproducing an optical fiber preform using the same.

BACKGROUND ART

In general, the optical fiber preform is produced by modified chemicalvapor deposition (MCVD), outside vapor deposition (OVD) or vapor axialdeposition (VAD) in which the preform is directly grown on the tip of aquartz bar.

The MCVD, the most widely used one of these methods, forms an opticalfiber preform by depositing a core layer and a clad layer havingdifferent refractive indices in a quartz tube of a high purity. Here,the refractive indices are controlled by adjusting composition rates ofdeposited substances. That is, the refractive indices of the core andclad layers are controlled by differently adjusting the deposition rateof GeO₂ to SiO₂ in the composition used for the deposition of the coreand clad layers.

The composition is usually supplied into the quartz tube by carriergases and deposited while the outer surface of the quartz tube is heatedto a temperature between 1300 to 1700° C. by a heat source such as gastorch. The gaseous reactant becomes the soot of SiO₂ and GeO₂ at such ahigh temperature.

While the soot of SiO₂ and GeO₂ passes through the quartz tube in theaxial direction of the tube, a part of the soot is deposited on the wallof the quartz tube by thermophoresis and the rest thereof is dischargedto the outside through a soot exhaust tube. The quartz tube with thesooty substance deposited on the wall is subjected to a collapsingprocess to produce a preform rod in the form of a cylinder and then aclosing process to complete the entire process, thereby producing anoptical fiber preform. Here, the quartz tube which is used to formoptical fiber preform is called a substrate tube.

In recent years, there is a trend toward increased used of a horizontallathe in the deposition process. A primary preform prepared in thedeposition process using the horizontal lathe is subjected to thecollapsing process and the closing process to form an optical fiberpreform.

FIG. 1 is a schematic view of a conventional apparatus for producing anoptical fiber preform in which deposition process according to themodified chemical vapor deposition method is performed.

As shown in FIG. 1, the conventional apparatus for producing an opticalfiber preform includes a substrate tube 10, chucks 20 for holding hotends of the substrate tube 10, supporting portions 30 for supportingrespective chucks, a horizontal lathe 40 on which the support portions30 are fixedly mounted, a main heat source 50 disposed on the horizontallathe 40 between the supporting parts for beating substrate tube 10, agas supply device 60 disposed outside the horizontal lathe for supplyinggases to one end of the substrate tube 10, and a soot collector 70disposed outside the horizontal lathe for collecting soot dischargedThrough a soot exhaust tube connected to the other end of the substratetube.

Since the methods for producing an optical fiber preform by theconventional apparatus for producing an optical fiber preform having theabove construction involve a high temperature deposition process, themechanical strength and viscosity of the substrate tube 10 are reduced.Thus, in the process for producing a preform, the deposition should becarried out at a uniform rate and the outside diameter of the substratetube 10 should be kept uniform while minimizing the deformation of thesubstrate tube 10 in the radial direction. However, the optical fiberpreform produced by the conventional methods has elastic deformation andviscous deformation at the same time. That is, the finally producedsubstrate tube 10 deflects in proportion to the elastic deformationlevel, deposition time and viscous deformation level.

FIG. 2 is a schematic view showing the deflection phenomenon of thesubstrate tube 10 produced by the conventional apparatus for producingan optical fiber preform, wherein the substrate tube deflects more whenthe deposition process is carried out repeatedly.

Moreover, the substrate tube and the deposition time should be longerwith a higher temperature for mass production, and it makes deflectionphenomenon of the substrate tube 10 to be severer. Thus, when thedeflection of the substrate tube 10 is excessive, the production of anoptical fiber preform itself is impossible, or the produced opticalfiber preform, where it may be produced, cannot properly shows itsfunction.

DISCLOSURE OF INVENTION

Thus, the present invention has been made in view of the above problems,and it is an object of the present invention to provide an apparatus forproducing an optical fiber preform with an additional support for asubstrate tube 100 which has been heated by a main heat source 500 for apredetermined period of time to prevent the substrate tube 100 fromdeflecting in the deposition process of modified chemical vapordeposition and a method for producing an optical fiber preform using thesame.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided an apparatus for producing anoptical fiber preform to perform the deposition process by modifiedchemical vapor deposition comprising a main heat source locationdetecting sensor 800, an additional supporting device control part 1000electrically connected to the main heat source location detecting sensor800 by wired or wireless means and an additional supporting device 1100electrically connected to the additional supporting device control part1000 by wired or wireless means.

An apparatus for producing an optical fiber preform using MCVD (ModifiedChemical Vapor Deposition) that deposits deposition compositions on aninner surface of a substrate tube by heating an outer surface of thesubstrate tube supported by a horizontal lathe with the use of a mainheat source moving along the horizontal lathe, the apparatus comprisingan additional supporting device including a substrate tube additionallysupporting part for supporting the substrate tube in a load direction incontact with the substrate tube, a vertical transport member fortransporting the substrate tube additionally supporting partperpendicularly to an axial direction of the substrate tube additionallysupporting part, and a horizontal transport member for transporting thevertical transport member to the axial direction; a main heat sourcelocation detecting sensor for detecting a location of the main heatsource; a supporting location control sensor for detecting a location ofthe additional supporting device when the additional supporting devicereaches a predetermined supporting location; and an additionalsupporting device control part for receiving a signal indicative of thelocation of the main heat source from the main heat source locationdetecting sensor and then moving the additional supporting device usingthe transport member, the additional supporting device control partcontrolling the vertical transport member to raise the substrate tubeadditionally supporting part perpendicularly to the axial direction andthus support the substrate tube.

In order to achieve the above object, according to another aspect of thepresent invention, there is also provided a method for producing anoptical fiber preform to perform the deposition process of modifiedchemical vapor deposition, comprising the steps of: heating a substratetube 100 from initial part to the ending part by a main heat source 500(S1); identifying the location of the main heat source 500 by a mainheat source location detecting source 800 (S2); moving a additionalsupporting device 1100 to a predetermined location (S3 and S4);supporting the substrate tube 100 until the temperature of substratetube reaches the target value after the main heat source 500 startsheating the substrate tube (S5); and returning the additional supportingdevice 1100 to its original location (S6).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be apparent from the following detailed description ofthe preferred embodiments of the invention in conjunction with theaccompanying drawing, in which:

FIG. 1 is a schematic view of a conventional apparatus for producing anoptical fiber preform;

FIG. 2 is a schematic view showing the deflection phenomenon of asubstrate tube produced by the conventional apparatus for producing anoptical fiber preform;

FIG. 3 is a schematic view of an apparatus for producing an opticalfiber preform according to an embodiment of the present invention;

FIG. 4 is a schematic view of an apparatus for producing an opticalfiber preform according to an embodiment of the present invention,wherein a substrate tube is supported;

FIG. 5 is a schematic view of an apparatus for producing an opticalfiber preform according to an embodiment of the present invention,wherein a piston of an additional supporting device descends;

FIG. 6 is a flow chart illustrating the operation of a main heat sourceand an additional supporting device according to a first embodiment ofthe method for producing an optical fiber preform of the presentinvention; and

FIG. 7 is a flow chart illustrating the operation of a main heat sourceand an additional supporting device according to a second embodiment ofthe method for producing an optical fiber preform of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention is described in detail.

FIG. 3 is a schematic view of an apparatus for producing an opticalfiber preform according to an embodiment of the present invention andFIG. 4 is a schematic view of an apparatus for producing an opticalfiber preform according to an embodiment of the present invention,wherein a substrate tube is supported.

As shown in FIG. 3, the apparatus for producing an optical fiber preformaccording to the present invention comprises a main heat source 500disposed on a horizontal lathe for applying heat to a substrate tube, amain heat source location detecting sensor 800 fixed on a side of thehorizontal lathe or disposed at a predetermined distance from thehorizontal lathe for detecting the location of the main heat source, anadditional supporting device 1100 disposed on the horizontal lathe forsupporting the substrate tube, and an additional supporting devicecontrol part 1000 disposed outside the horizontal lathe for wiredly orwirelessly receiving a location signal from the main heat sourcelocation sensor 800 and controlling the additional supporting device inresponse to the received location signal. Here, the additionalsupporting device 1100 functions to wiredly or wirelessly receive acontrol signal from the additional supporting device control part 1000to be moved to a predetermined supporting location in response to thereceived control signal.

As shown in FIG. 4, the additional supporting device 1100 comprises asubstrate tube additionally supporting part 1400 for additionallysupporting the substrate tube 100, a vertical transport means having thesubstrate tube additional supporting part 1400 attached thereto totransport the substrate tube additionally supporting part 1400perpendicularly to the axial direction of the substrate tube 100 inresponse to a control signal transmitted thereto from the additionallysupporting device control part 1000, and a horizontal transport meanshaving the vertical transport means attached thereto to transport thevertical transport means to the axial direction of the substrate tube100 in response to a control signal transmitted thereto from theadditional supporting device control part 1000.

The substrate tube additionally supporting part 1400 comprises a pair ofrolls 1200 for supporting the substrate tube 100 in such a manner as tobe in contact with the substrate tube 100 and a roll supporting part1300 on which the rolls 1200 are mounted. Here, the roll supporting part1300 is attached to a rotating arm 1500, whereby it may rotate within apredetermined angle range.

In an embodiment according to the present invention, the verticaltransport means is realized by a pneumatic cylinder 1700, though variousmeans having the same function as the pneumatic cylinder may beemployed.

The pneumatic cylinder 1700 is wiredly or wirelessly connected to theadditional supporting device control part 1000 for receiving anelectrical control signal therefrom and lifting up a piston 1600 inresponse to the received control signal to actuate the rotating arm 1500mounted to an end of the piston 1600 with a rotative joint.

The horizontal transport means comprises a transport stand 1900 having apinion shaft 2400 fastened to a drive shaft 2200 and a pinion 2300mounted on the pinion shaft 2400, and a guide 1800 disposed on ahorizontal lathe 400 to be engaged with the pinion 2300 and having arack formed thereon. Here, the drive shaft 2200 drives the pinion 2300.

In a preferred embodiment according to the present invention, thehorizontal transport means further comprises a drive means.

The drive means includes a rotation controllable motor wiredly orwirelessly connected to the additional supporting device control part1000. The motor may be preferably realized by a constant speed motor2000, a precisely controllable servo motor or a stepping motor, thoughany other motors having the same function as them may be employed.

The additional supporting device control part 1000 is wiredly orwirelessly connected to a supporting location control sensor 900 andcomprises a first input part for receiving a signal indicative oflocation of the main heat source 500 from the main heat source locationdetecting sensor 800, a second input part for receiving a signalindicative of the additional supporting device 1100 reaching thesupporting location from the supporting location control sensor 900, amicroprocessor for controlling the operation of the motor and pneumaticcylinder 1700 installed in the additional supporting device 1100 and anoutput part for outputting an operation control signal generated fromthe microprocessor. Here, the supporting location control sensor 900 isfixed at the supporting location predetermined on the horizontal latheor located at a predetermined distance from the horizontal lathe. Italso detects the location of the additional supporting device 1100 whenthe additional supporting device 1100 reaches the predeterminedsupporting location and transmits a location signal to the second inputpart.

The microprocessor makes the additional supporting device 1100 supportthe substrate tube 100 only for a predetermined period of time until thetemperature of substrate tube reaches the target value after the mainheat source 500 starts heating the substrate tube.

The additional supporting device 1100 according to the present inventionreduces the effective length of the substrate tube 100 among factorswhich most affect the deformation of the substrate tube 100, includingthe effective length, which means a distance between supported points ofthe substrate tube 100, the shape of the substrate tube 100, the timeduring which the substrate tube is exposed to the heat source, and thelike. Therefore, the deflection at a portion where the initial part hasa low viscosity and the effect of shear force is great can beconsiderably reduced. Theoretically, when a beam is under its ownweight, the deformation generated at an end of the beam is in proportionto 4th power of the length of the beam and hence, the additionalsupporting device according to the present invention can reduce 4thpower of the length reduction.

Now, the operation of the apparatus for producing an optical fiberpreform according to the present invention having the foregoingconstruction will be described in detail hereafter with reference toFIGS. 4 and 5.

As shown in FIGS. 4 and 5, when the first input part receives a locationsignal of the main heat source 500, the microprocessor drives theconstant speed motor 2000 to transport the additional supporting device1100. When the second input part receives the signal indicative of theadditional supporting device reaching the supporting location from thesupporting location control sensor 900, the microprocessor stops thetransport of the additional supporting device 1100 and controls to liftup the piston 1600 of the pneumatic cylinder 1700. As the piston 1600 israised, the rotating arm 1500 is actuated and consequently, thesubstrate tube additionally supporting part 1400 is raised toadditionally support the substrate tube 100

In a modified embodiment of the present invention, the additionalsupporting device 1100 may be moved manually by rotating a rotator 2100connected to the pinion axis 2400 as shown in FIG. 4 and FIG. 5, insteadof using a constant speed motor.

Now, the method for producing an optical fiber preform according to thepresent invention will be described in detail hereinafter with referenceto FIGS. 6 and 7.

FIG. 6 is a flow chart illustrating the operation of a main heat sourceand an additional supporting device according to a first embodiment ofthe method for producing an optical fiber preform of the presentinvention.

First, the main heat source 500 heats the substrate tube 100 from theinitial part where the heating is initiated to the ending part where theheating is ended (S1). After an elapse of a prescribed time, thesubstrate tube 100 comes to have uniform heat flux. When the temperatureof the tube exceeds a predetermined limit, the tube begins to deflect atthe heating point. At this time, the main heat location detecting sensor800 disposed at the initial part of the substrate tube 100 identifiesthe location of the main heat source (S2). Then, the main heat locationdetecting sensor 800 transmits a location signal to the additionalsupporting device control part 1000, which in turn controls to start thetransport of the additional supporting device 1100 (S3). Thus, theadditional supporting device 1100 is moved to a predetermined supportinglocation (S4).

Then, the additional supporting device supports the substrate tube 100until the temperature of substrate tube reaches the target value afterthe main heat source 500 starts heating the substrate tube 100 by meansof a timer (S5) and returns to its original position (S6).

Therefore, the method for producing an optical fiber preform accordingto the present invention makes it possible to produce an optical fiberpreform with a minimized deflection of the initial part.

Meanwhile, an optical fiber preform can be produced according toprocedures as shown in FIG. 7 according to the operation mode of themain heat source.

FIG. 7 is a flow chart illustrating the operation of a main heat sourceand a additional supporting device according to a second embodiment ofthe method for producing an optical fiber preform of the presentinvention, which further comprises a step of allowing the main heatsource to heat the substrate tube between the step (S1) and the step(S2). Thus, the method for producing an optical fiber preform accordingto the second embodiment is carried out as follows. The main heat source500 heats the substrate tube 100 from the initial part where the beatingis initiated and the ending part where the heating is ended (S10).Thereafter, the main heat source 500 returns from the ending part to theinitial part with heating (S20). The main heat location detecting sensor800 mounted on the horizontal late at the initial part of the substratetube 100 then identifies the location of the main heat source 500 (S30).Then, when the additional supporting device control part 1000 receives alocation signal of the main heat source 500 from the main heat locationdetecting sensor 800, it starts the additional supporting device 1100(S40). Next, when the additional supporting device control part 1000receives a location signal of the additional supporting device from thesupporting location control sensor 900, it allows the additionalsupporting device 1100 to be moved to a predetermined supportinglocation in response to the received locations signal (S50).

Once the additional supporting device 1100 is moved to the supportinglocation where the supporting location control sensor 900 is disposed,it supports the substrate tube 100 until the temperature of substratetube reaches the target value after the main heat source 500 startsheating the substrate tube 100 by means of a timer (S60) and, after anelapse of a prescribed time, returns to its original position (S70).Again, the main heat source 500 heats the substrate tube 100 whilemoving from the initial part to the ending part (S10) and returns fromthe ending part to the initial part (S20), after which the forgoingprocedures are performed repeatedly.

Here, the supporting location is determined in consideration thestandard of the substrate tube 100, deposition time or viscosity.

Therefore, the method for producing an optical fiber preform accordingto the present invention makes it possible to produce an optical fiberpreform without deflection of the initial part.

INDUSTRIAL APPLICABILITY

The apparatus for producing an optical fiber preform and the method forproducing an optical fiber preform using the same according to thepresent invention reduce the effective length of the substrate tube 100by additionally supporting the substrate tube 100, thereby minimizingthe deflection of the substrate tube 100. Particularly, it is possibleto considerably reduce the deflection of the substrate tube at itsinitial part and thus to achieve a high deposition efficiency.Accordingly, it is possible to mass-produce an optical fiber preform ofhigh quality.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. An apparatus for producing an optical fiber preform using MCVD(Modified Chemical Vapor Deposition) that deposits depositioncompositions on an inner surface of a substrate tube by heating an outersurface of the substrate tube supported by a horizontal lathe with theuse of a main heat source moving along the horizontal lathe, theapparatus comprising: an additional supporting device including asubstrate tube additionally supporting part for supporting the substratetube in a load direction in contact with the substrate tube, a verticaltransport member for transporting the substrate tube additionallysupporting part perpendicularly to an axial direction of the substratetube, and a horizontal transport member for transporting the verticaltransport member to the axial direction; a main heat source locationdetecting sensor for detecting a location of the main heat source; asupporting location control sensor for detecting a location of theadditional supporting device when the additional supporting devicereaches a predetermined supporting location of the axial direction; andan additional supporting device control part for receiving a signalindicative of the location of the main heat source from the main heatsource location detecting sensor and then moving the additionalsupporting device using the horizontal transport member, the additionalsupporting device control part controlling the vertical transport memberto raise the substrate tube additionally supporting part perpendicularlyto the axial direction and thus support the substrate tube.
 2. Theapparatus producing an optical fiber preform according to claim 1,wherein the substrate tube additionally supporting part includes; a pairof rolls for supporting the substrate tube in contact with the substratetube; and a roll supporting part on which the rolls are mounted.
 3. Theapparatus producing an optical fiber preform according to claim 2,wherein the vertical transport member includes; a rotating arm connectedto the substrate tube additionally supporting part; a piston hinged armconnected to the substrate tube additionally supporting part; apneumatic cylinder for wiredly or wirelessly receiving an electriccontrol signal from the additional supporting device control part andlifting up the piston.
 4. The apparatus for producing an optical fiberpreform according to claim 2, wherein the horizontal transport memberincludes; a constant speed motor whose rotation is controlled by theadditional supporting device control part; a pinion connected to theconstant speed motor; and a rack engaged with the pinion.